1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method for controlling UpLink (UL) transmit power, when a plurality of UL transmission channels are transmitted simultaneously.
2. Background Art
Future-generation multimedia wireless communication systems, which are a recent active research area, require processing of various types of information including video data and wireless data at high data rates, beyond the traditional voice-oriented service.
Owing to its advantage of high data rate, Orthogonal Frequency Division Multiplexing (OFDM) has recently attracted much attention. OFDM is a special case of Multi-Carrier Modulation (MCM) in which a frequency band is divided into multiple orthogonal subcarriers and data is transmitted on the subcarriers. The low complexity of OFDM reduces inter-symbol interference. In OFDM, an input serial sequence of data symbols is converted to N parallel data symbols and transmitted on N separate subcarriers.
Orthogonality is maintained among the subcarriers in the frequency domain. Each orthogonal channel experiences mutually independent frequency-selective fading and the resulting increase in the gap between transmitted symbols leads to minimum inter-symbol interference. Orthogonal Frequency Division Multiple Access (OFDMA) is a multiple access scheme in which multiple accesses are allowed through independent allocation of part of available subcarriers to each user in an OFDM system. In OFDMA, it is typical to independently allocate frequency resources, namely subcarriers to a plurality of users in such a manner that the frequency resources are not overlapped with one another. As a result, allocation of frequency resources is mutually exclusive among users in OFDMA. The OFDMA system may achieve frequency diversity for multiple users by frequency selective scheduling and allocate subcarriers in various manners according to subcarrier permutation.
In some wireless communication systems, a UL control channel carrying a control signal from a User Equipment (UE) to a Base Station (BS) may be physically distinguished from a UL data channel carrying data from the UE to the BS. A plurality of control channels and/or data channels may be transmitted in one symbol. The transmit powers of UL transmission channels each may be determined using a predetermined equation.
In general, a maximum available transmit power is predetermined for UL transmission of a UE according to a bandwidth allocated to the UE, the throughput of the UE, the battery performance of the UE, etc. Hence, if a total transmit power required to transmit a plurality of transmission channels exceeds the maximum available transmit power of the UE, the UE may not transmit the plurality of transmission channels successfully.
Accordingly, there exists a need for a method for effectively allocating transmit power to a plurality of UL transmission channels that are to be transmitted simultaneously in different physical areas.